The present invention relates generally to the field of spacecraft power sources, and more particularly to thermophotovoltaic power sources.
There is a continuing interest in the spacecraft arts in finding a power supply which is more durable and reliable than the standard solar cell panels presently utilized. Solar cell power supplies are of concern because they are subject to severe performance degradation from charged particles. Since future space missions will be required to operate in the Van Allen belts which contain large numbers of geomagnetically trapped electrons and protons, the use of solar cell panels for such missions will be severely limited. In addition, the solar cells are also susceptible to degradation due to the charged particles generated by solar flare events. Finally, solar cell panels will be susceptible to performance degradations due to energetic electron emission from floating radioactive debris in the event of atomic weapon detonations in the atmosphere during wartime.
Radioisotope energy sources have been considered as alternatives to the solar cell panels currently in use. However, the complexity of final fabrication, integration, and launch operations in combination with the risk of an accidental unplanned spacecraft dissent with such a radioactive power source mediates against the use of such an energy source.
Nuclear powered thermoelectric and thermionic systems have been considered as alternative power supplies. However, these types of electric energy conversion techniques require the energy conversion element to operate at extremely high temperatures. These high temperatures place a major limit on useful lifetimes of the power supplies and also pose major reliability problems.
The energy converting element of a thermovoltaic power source, in contradistinction to the above, operates at near room temperature and thus promises high reliability over a long service lifetime. Thus, thermophotovoltaic power supplies are being actively considered for use aboard spacecraft. A thermophotovoltaic power supply typically consists of a moderately high density energy source in intimate thermal contact with a radiating surface, to thereby raise the radiator temperature to substantial values, usually above 1,000 K. The thermal radiation from this hot surface then falls upon an array of photovoltaic cells, which converts a portion of this energy to useful electric power. The photovoltaics, which differ from the more well-known solar cells in that they are designed to respond optimally to the thermal radiation spectrum instead of the solar spectrum, are typically kept at moderate operating temperatures (e.g., room temperature) by the use of a waste heat elimination system.
The present system utilizes solar radiation as the primary energy source. Accordingly, one of the problems with such a system is that the primary energy input to the device will diminish to zero when the spacecraft is in that portion of its orbit where the sun is eclipsed by the earth. Additionally, such a solar powered system suffers from the inability to adjust its operating level with the load. Without a provision for varying the operating level, the system must be designed with the highest load anticipated, thereby wasting power during lower load periods.